Transverse-flow pyrocatalytic reactor for conversion of waste plastic material and scrap rubber

ABSTRACT

A process for converting organic waste into reusable hydrocarbons and a system for doing so, the system including a feeding mechanism for the waste, a reactor and a residue-disposing mechanism. The waste is to be fed into the reactor in which a molten lead bath is confined in an oxygen-free atmosphere. The system is used to practice a process for the pyrocatalytic conversion of the waste, which process comprises, feeding the waste into a reaction zone of a pyrocatalytic reactor, the waste being essentially free of a halogenated synthetic resinous material, and mixing the waste with a minor proportion by weight of a particulate catalyst in the bath held at a temperature in the range from about 450° C. to 550° C. in an elongated vat. The catalyst consists essentially of a major proportion by weight of particulate bauxite &lt;2 mm, in combination with a minor proportion of aluminum powder &lt;0.1 mm having a minimum nominal aluminum content of at least 95%, preferably at least 98%, and a Fe content of less than 0.5% and Si less than 0.2%. Between the feed-inlet or “charging” end of the vat where waste from the feeding mechanism enters and the “residue-discharging” or “discharging” end of the vat where the residue is delivered to the residue-disposing mechanism, a combination of plural rotating drums with radially protruding fingers in cooperation with gratings, provide the necessary mixing and urging action and contact time. The waste in the molten lead is urged along the vat&#39;s longitudinal axis starting near the charging end of the vat. The length of the vat is sufficient to afford a residence time for the waste of no more than one hour in the vat, and the depth of molten lead in it is at least 10 cm, preferably 30 cm above the surfaces of heating tubes disposed in the molten lead. Thus, the waste is thermally and catalytically converted with at least 60% effectiveness into reusable hydrocarbons which are removed as vapor from above the melt in the reaction zone and recovered as reusable hydrocarbons.

Field of the Invention: The present invention relates to an improvementin a pyrolysis reactor wherein organic waste is catalytically convertedinto hydrocarbons which are recovered as vapor issuing from a moltenlead bath. “Organic waste” or “waste” for brevity, refers herein to apredominantly hydrocarbon synthetic resinous materials, substantiallyfree of halogen-containing resins, referred to herein as “plastics”,and, rubber from scrap tires.

The plastics or rubber are mixed with a unique catalyst as the mixtureis moved along the heated molten lead along the length of the bath,longitudinally from the bath's feed-inlet end to its residue-dischargeend, while the bath is heated with a heating medium flowing first in alongitudinal direction, then in a direction transverse to the flow ofwaste. The reactor is therefore referred to as a “transverse-flowpyrocatalytic” reactor. The transverse direction is referred to hereinas the “x”-axis, the longitudinal axis is referred to as the “y”-axisand the vertical direction is referred to as the “z”-axis. Vapors ofhydrocarbons generated within the reactor, which vapors are readilycondensible in a cold water heat exchanger, are recovered in aconventional recovery system. The recovered, condensed hydrocarbons arepreferably further conventionally refined for use as diesel fuel,gasoline and heating oil; and the non-condensible hydrocarbons, alongwith carbon monoxide and carbon dioxide are preferably recycled as agaseous recycle stream to provide fuel for burners used to generate hotgases to heat the bath.

BACKGROUND OF THE INVENTION

The Problem: Molten lead, used as a heating medium to pyrolyze plasticsand rubber waste in the prior art, presents unique problems because leadis about 11.5 times heavier than the waste—the waste is quickly forcedto the surface preventing contact time with the lead long enough toconvert the waste in a reasonable amount of time. Particularly whensolid waste includes polyolefins, poly(vinyl aromatic)s, and rubber fromworn out tires, it is difficult to provide an economical level ofconversion to reusable hydrocarbons within a residence time (in themolten bath) of less than 1 hour, preferably less than 30 min. “Reusablehydrocarbons” refers to both higher molecular weight hydrocarbons whichare condensed, and lower molecular weight hydrocarbons which can berecycled as fuel. Reusable hydrocarbons consist of a major proportion byweight of condensible C₅ ⁺ hydrocarbons (having at least five carbonatoms) and a minor proportion (relative to the C₅ ⁺ hydrocarbons) ofnon-condensible C₁-C₄ hydrocarbons, typically less than 20% by weight ofthe C₅ ⁺ hydrocarbons, the components in the vapor phase being inequilibrium with those in the condensate at the temperature and pressureconditions of condensation within the condenser.

Though a molten lead bath is able to provide a source of heat at achosen, substantially constant temperature, using molten lead (or“melt”) as a heat transfer medium in a substantially oxygen-freeatmosphere in the reactor, presents numerous difficulties. To beginwith, a floating layer of organic waste acts as an insulating barrier,preventing pieces of waste within the floating layer from being heatedsufficiently to depolymerize. If the waste cannot be adequatelycontacted with the melt it does not matter how much melt is in the bath.Yet, efficient heat transfer from the melt to the waste, to obtain aneconomic residence time in the melt, must not interfere with being ableto transport the waste longitudinally through the melt. To cope withthis problem by providing a high enough bath temperature to effect thepyrolysis in a reasonable amount of time, results in too high aproduction of hydrocarbons lower than C₄, appreciable CO and CO₂. Tocomplicate the problem, when using a solid, particulate, catalyst it iscritical that the waste be contacted and mixed with both the catalystand the melt.

When such a catalyst is a combination of an aluminum powder and aluminumoxide mineral, whether calcined hydrated alumina, or calcined zeolite,this mixing is difficult to do without using a fluid bed. “Zeolite”refers to a natural or synthetic composition typically having thestructure M_(x/n)[(AlO₂)_(x)(SiO₂)_(y).zH₂) where n is the charge of themetal cation, M^(n+), which is usually Na⁺, K⁺, or Ca²⁺, x and y areintegers, typically having substantially the same value in the rangefrom 2 to 10, and the z is the number of moles of water of hydration.

Since conversion of scrap rubber generates sulfur and sulfur-containingcompounds, the catalyst, most preferably a combination of aluminumpowder and calcined bauxite powder, is required to be substantiallyunreactive with both, the sulfur and sulfur-containing compounds, andchlorine and hydrochloric (HCl) acid gases, if such gases are present inan appreciable amount. In addition, the reactor requires an essentiallyoxygen-free atmosphere within it; and the high specific gravity of leadprecludes using very much of the melt in the bath, for practical costconsiderations relating to the structural requirements of a vat ortrough in which the molten lead bath is held.

Moreover, though the housing and other components of the reactor aretypically made of acid and heat-resistant sheet steel, e.g. H25N20S2,the steel does not have notably long-term resistance to SO₂, H₂SO₃,chlorine and HCl gases. The reliance on affordable steel and the use ofaluminum powder in the catalyst requires feeding plastic substantiallyfree of a halogen-containing synthetic resin, to the reaction zone, ifsafe, long-term operation of the reactor is sought. By “substantiallyfree of a halogen-containing synthetic resin” is meant that less than 5%by weight of the waste is a polymer containing chlorine, bromine, iodineor fluorine, e.g. poly(vinyl chloride) (“PVC”) scrap, or otherhalogen-containing synthetic resins, e.g. chlorofluoro-, chlorobromo-and fluorocarbon polymers.

The Prior Art:

Molten metal, particularly lead, has been the heat transfer medium ofchoice for the thermal conversion of organic matter, generally. Theproblem of heating organic matter which floated on a molten lead bathwas recognized as early as before 1926 when U.S. Pat. No. 1,601,777disclosed moving crushed shale along the undersurface of a slightlyinclined apertured member, beneath the surface of a heated bath. U.S.Pat. No. 2,459,550 addresses the problem by confining wood or coalpieces between two endless screens. U.S. Pat. No. 3,977,960 teachesusing angularly inclined screw conveyors to force crushed shale into amolten bath. As recently as 1990, U.S. Pat. No. 4,925,532 teaches movingperforated baskets filled with waste on an endless conveyor; the basketsare hooked to the conveyor to prevent them from floating against guiderails above the baskets. The '532 patent teaches that it is criticalthat the molten lead bath be maintained above 343° C. (650° F.),ignoring the fact that the melting point of pure lead at atmosphericpressure is just below, i.e. 327.5° C. (621.5° F.). It failed to realizethat a catalyst could enhance conversion; and it missed the fact thatoptimum conversion of polyolefins, polystyrene and scrap from tires, tovapor consisting essentially of a major proportion by weight of C₅ ⁺hydrocarbons occurs only in the narrow range from 450° C.-550° C. (842°F.-1022° F.), a range commencing more than 100° C. above the temperaturedeemed critical. Most recently, in 1992, U.S. Pat. No. 5,085,738 teachesusing a long, upwardly inclined oxygen-free cylindrical chamber filledwith molten lead, through which chamber pieces of scrap tires areforced. A ram is used to circumvent the problem of floating rubber, butstill relying solely on the thermal pyrolysis of the submerged rubber.The prior art countered the high specific gravity of molten lead byconfining the charge in the melt. It ignores the problem of essentiallyinstantly solidifying molten lead on the rubber as it is fed, because ofthe low heat capacity (and specific heat) of the lead; and, therequirement of timely supplying adequate heat to re-melt the lead.

It will be evident that the invention disclosed herebelow, for feedingthe waste to the reactor, converting the waste in the reactor, removingand disposing of the residue, is based on the use of a unique catalystin combination with a novel and unexpectedly efficient system of dealingwith the numerous problems associated with feeding waste and catalyst toa molten lead bath in a sealed environment, including, for practicaloperation of the reactor, not submerging the waste in the molten lead.Further, not unexpectedly, the prior art processes and apparatus whichrely solely on thermal pyrolysis of plastics and rubber in molten lead,are conspicuously devoid of data showing the effectiveness of theconversions obtained. As will be evident from the data presented below,the conversion of waste to reusable hydrocarbons by pyrolysis in moltenlead alone, is only 53% (see Table 1) when the scrap is PE(polyethylene) and PP (polypropylene); and more than 90% when thecatalyst used is bauxite/Al=97/3.

Recognizing the advantage of using an effective catalyst for theconversion of waste polyolefins, polystyrene and the like tohydrocarbons, U.S. Pat. No. 4,851,601 teaches using a fluid bed ofzeolite particles, as does Chinese patent application WO95/06682. Ineach case, hydrocarbons having a wide range of boiling points arecollected, but they rely on the efficient heat transfer provided by afluid bed and the catalytic effect of a zeolite only, and the zeolite,by itself is evidently unaffected by the presence of chlorine in PVC.

SUMMARY OF THE INVENTION

The conversion of substantially halogen-free waste to desirablehydrocarbons is effected by providing an elongated generally rectangularvat or trough in which molten lead is held within a sealed, essentiallyoxygen-free housing, and the waste is contacted with a catalystconsisting of a combination of an aluminum oxide mineral powder <2 mmdiameter, and essentially pure aluminum powder <0.1 mm diameter, whilethe waste is being heated with the melt. The catalytic action isevidently provided by the interaction of the pure aluminum and thealuminum oxide molecules. The aluminum mineral oxide powder ispreferably calcined to avoid generating water from uncalcined oxide inthe melt.

Waste, preferably compacted and fed unconfined to the inlet of the vat,floats on the melt and is mixed and tossed with a reciprocable steelgrating while the waste is urged from one end of the vat to the other,being advanced longitudinally through the vat, without the waste beingsubmerged in the melt. The steel grating moves from a position under thesurface of the melt where it is heated, to a position above the meltwhere the grating transfers the heat to the waste. This feature,utilizing the much higher heat capacity of steel (nearly three timeshigher than that of lead) overcomes the problem of having molten leadsolidify, essentially instantly, on the waste when it is submerged inthe melt. Such solidification results because the rate of heat transferfrom the melt to the waste is so high. Such waste, with lead solidifiedon it, must then be transported while being heated to liquefy the melt.Though submerging the waste in the melt will have the same thermalresult, in a commercial reactor to which more than 1000 Kg/hr of wasteis fed, it is difficult to move so much waste, with solidified lead onit, through the vat; and it is not practical to heat so much waste, withsolidified lead on it, at a rate high enough to re-melt the lead on thewaste and obtain an economical residence time.

The waste is intermittently advanced by using at least one, preferablyplural, laterally spaced-apart rotatable drums, each provided withradially protruding blades which urge waste on the surface of the moltenlead longitudinally along the length of the trough. Simultaneously, thewaste is bathed with melt scooped up from near the surface of the bath.Because, as the waste is converted, the amount of floating waste isprogressively reduced, the axis of rotation of each drum is lower thanthe preceding drum, that is, the axis of each successive drum isprogressively vertically downwardly spaced-apart.

The use of the reciprocable mixing grating in cooperation with eachdrum, except the first near the inlet of the vat, urges waste upwardstowards the drum and bathes floating waste with molten lead, thusproviding the contact necessary to convert the-waste while dealing withsolidifying lead; simultaneously, “fingers” on the drum advance thewaste through the vat. It is this unique mechanism for urging thefloating waste through the molten bath without submerging the waste inthe bath, in combination with the catalytic action of the catalyst used,and the essentially constant temperature of the molten lead held in adesired range of temperature, which accounts for the success of thiswaste-conversion process. High conversions to desirable hydrocarbons,and avoiding the formation of all but a relatively small amount ofcarbonaceous residue, is effected by choosing the appropriatetemperature to match the waste being fed. Depending upon how clean thewaste is, the residue will also contain stones, pieces of wire fromscrap tires, pieces of stray metal, glass and other solids notdecomposed at the temperature of the molten lead. The residue iscontinuously removed from the reactor with an endless chain conveyor.

Either crushed calcined bauxite alone, or aluminum powder alone, isinsufficiently effective as a catalyst to convert waste, even when >90%(more than 90 percent) of the bauxite particles are <1 mm in diameter,and >90% of the aluminum powder particles are <0.1 mm (at least an orderof magnitude smaller than bauxite). “Diameter” refers to the equivalentdiameter of a particle. However, when a mixture consisting essentiallyof a major proportion by weight of the same bauxite is combined with aminor proportion of the same aluminum powder and contacted with both theheated waste and molten lead, the combination catalyst is typically morethan 60% effective to convert the waste into reusable hydrocarbons.Unexpectedly, the substantially halogen-free, reactive atmosphere ofhydrocarbons within the reactor, boosts the effectiveness of thealuminum powder rather than negating it.

Contact with molten lead, by waste and catalyst, both of which are muchlighter than lead, is ensured by using a combination of successive drumswith radially protruding mixing fingers which engage the waste in thefloating layer as it is moved upwards by a grating. The grating is partof a U-shaped saddle forming a cooperating mixing and bathing assembly.The grating reciprocates at a slight angle, less than 30° to thevertical, heats the waste by contact with it, and bathes the floatingwaste with melt scooped from the surface of the bath. This combinedaction of heating and bathing the waste with melt and also urging itlongitudinally along the length of the bath, allows conversion of thewaste with a residence time in the molten bath of less than 1 hour,preferably less than 30 min.

Though lead melts at 327.5° C. (621.5° F.), optimum effectiveness of thecatalyst is achieved at a temperature in the narrow range from about450° C.-550° C. (842° F.-1022° F.); conversions to reusable hydrocarbonsdrops off at temperatures below 450° C., but above 400° C., and above550° C. but below 600° C. where conversion to C₅ ⁺ hydrocarbonsdecreases, and to C₄ and lower hydrocarbons increases above 20%, andnormally negligible oxidation to CO and CO₂ increases.

A process for pyrocatalytic conversion of organic waste comprises,feeding waste into a reaction zone of a pyrocatalytic reactor, the wastebeing essentially free of a halogenated synthetic resinous material;mixing the waste with a minor proportion by weight of a catalyst in abath of molten lead held at a temperature in the range from 400° C. to600° C. in an elongated vat; recovering hydrocarbons generated in thereactor; and, removing carbonaceous residue. Thus, though the waste isunconfined, except by the surface of the melt, the waste is thermallyand catalytically converted with at least 50% effectiveness intoreusable hydrocarbon vapors which are condensed.

The catalyst consists essentially of a major proportion by weight ofbauxite powder, preferably calcined, in combination with a minorproportion of the aluminum powder having a minimum nominal aluminumcontent of at least 95%, preferably at least 98%, and a Fe content ofless than 0.5% and Si less than 0.2%. The amount of the catalystrequired is preferably no more than 20% by weight of the waste charged,preferably less than 10%, most preferably from about 0.5 to 5%.

The system for converting the waste comprises an elongated vat which isconfined in an essentially oxygen-free environment of the reactor; thevat has a feed-inlet or “charging” end and a “residue-discharging” or“discharging” end; the length of the vat is sufficient to afford aresidence time for the waste of no more than one hour, and the depth ofmolten lead in the vat is at least 10 cm. The waste on the molten leadis urged along the vat's longitudinal axis and bathed, substantiallysimultaneously, with melt. The contact of waste with melt is effected bya reciprocable grating moving into and out of the melt. Preferably, thereactor is fed with a feeding mechanism which compacts waste into a feedtube at the inlet of the reactor, forming an air-tight seal; andcarbonaceous residue is discharged by being compacted against aninclined plane and an adjustable continuous chain conveyor into aresidue-disposing assembly.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and additional objects and advantages of the inventionwill best be understood by reference to the following detaileddescription, accompanied with schematic illustrations of preferredembodiments of the invention, in which illustrations like referencenumerals refer to like elements, and in which:

FIG. 1 is an overall side elevational view schematically illustratingthe main components of the system.

FIG. 2 is a perspective view illustrating a mixing and bathing assemblyused to provide the necessary contact of waste and melt.

FIG. 2A is a detail of one effective embodiment of a mixing and urgingfinger welded to the surface of each mixing drum.

FIG. 3 is a cross-sectional view in the vertical plane 3-3 in FIG. 1,looking in the direction of the arrows, without showing the U-shapedsaddle under the drum.

FIG. 4 is a cross-sectional view of the reactor taken along the verticalplane 4-4 in FIG. 1 looking in the direction of the arrows.

FIG. 5 illustrates an embodiment of a feeding mechanism.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The key feature of the process is contacting the waste with acombination catalyst selected from the group consisting of a particulatecalcined hydrated aluminum oxide and a zeolite, mixed with aluminumpowder in a molten lead bath. The waste is typically selected from thegroup consisting of a polyolefin, e.g. PE and PP; a poly(vinylaromatic), e.g polystyrene; a polyamide, e.g. nylon; a rubber derivedfrom a conjugated diene, the diene having from 4 to 5 carbon atoms, e.g.polybutadiene and polyisoprene, whether natural or synthetic; and, arubber defined as a polyblock copolymer of a vinylaromatic compound anda conjugated diene, optionally hydrogenated to include a block of amonoolefin, the olefin having from 2 to 4 carbon atoms, e.g. Kraton®styrene-butadiene-styrene or “SBS” rubber. The term “aluminum oxidemineral” refers to minerals which contain a high amount of alumina, forexample the hydrated aluminas and the zeolites which arealumino-silicates. This combination catalyst, in which the preferredaluminum oxide mineral is a calcined hydrated alumina, results in apractical residence time of less than 1 hour results from mixing thewaste and forcefully urging it from the feed-charging or inlet end ofthe vat to the residue-discharging end of the vat.

Aluminum powder consists essentially of microgranules most of which havean equivalent diameter of less than 44 μm, each being essentially purealuminum (>99.5% Al) coated with a thin skin less than 0.1 μm thick(referred to as a “nanothick skin”). Such powder is preferably made byatomization of molten aluminum through small orifices in an atomizinghead immersed in molten aluminum. As molten aluminum flows through theorifices it strikes a stream of compressed air. This forms a spray ofaluminum melt which is quenched at rates on the order of 10² to 10⁸K/sec to form substantially spherical microgranules of pure Al coatedwith an aluminum oxide skin from 3 to 20 nm thick.

The most preferred finely divided aluminum oxide mineral is calcinedbauxite (and commercially available), though less readily availableparticulate gibbsite (a trihydrate), boehmite and diaspore(monohydrates), may also be used. When initially starting up the system,to facilitate catalytic conversion of the waste, catalyst is droppedonto freshly molten lead in the vat, from hatches (openings) in the roofof the reactor. Before feeding waste to the reactor it is mixed with asmall amount of additional catalyst so that the amount of catalyst inthe waste while it is in the reactor is in the range from about 0.5% to20%.

The preferred bauxite employed by the process is particulate bauxite,available in Poland as “Boksyt kalcynowany”, in a size range <1 mmhaving the following analysis: Al₂O₃—min 86% (typically 87.2%); Fe₂O₃—max 2% (typically max 1.6%); K₂O+Na₂O—max 0.25% (typically 0.18%) andSiO₂ —max 6% (typically 5.2%); the sp. gr. is in the range from 2.5-3.2,the bulk density is about 3.1 g/cc the apparent porosity is <10. Morethan 50% of all particles are in the size range from about 50 μm to 250μm, less than 10% being smaller than 50 μm, and the remaining being inthe range from 250 μm to 0.1 mm.

Aluminum powder is preferably metallurgical grade available fromBenda-Lutz Skawina having the following typical analysis: 99.7% Al;0.28% Fe; and 0.07 Si. A typical particle size distribution is asfollows: 77.6% >0.032 mm; 36.1% >0.063 mm; and 4.0% >0.09 mm. Theaverage particle diameter of the Al powder is in the range from about25-50 μm. Comparable aluminum powder is available from Alcoa in theGrade 100 and Grade 1200 series, among others.

A preferred ratio of the aluminum powder to bauxite powder is in therange from about 0.5-20% aluminum powder, preferably in the range fromabout 1-10% aluminum powder, most preferably less than 5%, there beingvery little economic improvement in conversion when the amount ofaluminum powder exceeds 10%.

Instead of mixing calcined aluminum oxide mineral, e.g. bauxite withaluminum powder, an alternative method for preparing the catalyst is byspraying a molten stream of aluminum at a temperature above 1200° C.onto a falling stream of bauxite particles in the size range givenabove. This results in the aluminum powder being adhered to andsupported on the particles of bauxite. In one embodiment, this may beachieved by mixing solid particles of aluminum metal into the flame ofan oxy-acetylene torch at a temperature in the range from about 2000° C.to 3000° C. and directing the flame at a falling stream of particles ofbauxite. The same may be done with any other aluminum oxide mineral,whether zeolite, gibbsite, etc.

The pyrocatalytic conversion of waste is most effective when the systemis fed with waste which is not “mixed” waste, but a particular class ofwaste, e.g. polyolefins; or polystyrene; or scrap rubber from vulcanizedpolybutadiene, polyisoprene and natural rubber in automobile, truck andaircraft tires. To a lesser extent, the catalyst is also effective withother poly(vinyl aromatic) resins, nitrile rubber, styrene-conjugateddiene-styrene rubber, acrylate rubber and other predominantlyhydrocarbon plastics. It is therefore desirable to sort the waste toprovide a particular material to be converted under temperatureconditions and a ratio of catalyst components specifically chosen forthat material.

Irrespective of the particular waste chosen, its specific gravity istypically about 1 or less, and, when fed into the molten lead, the wastewill be forcefully thrust to the surface, forming a waste layer whichfunctions as insulation, minimizing contact of all but the bottom of thelayer with the molten lead and catalyst.

Though any bath containing a predominant amount of lead may be used, alead bath containing less than 10% by weight of another metal ispreferred. Such a bath provides a high heat transfer coefficient, theheat content of the bath is rapidly exhausted as waste is converted, andthe heat must be just as rapidly replenished. The limitations thisplaces on the system are magnified by (i) heat conduction occurringprimarily in the vertical direction as the source of heat is from belowthe melt, and (ii) the layer of floating waste effectively insulatingthe upper portion of the layer from the heat in the melt. Therefore itis critical that, to meet an economic residence time of less than anhour, the floating waste be actively bathed with melt as the waste isurged along longitudinally along the surface of the melt.

It is not necessary, if the waste is polyolefin film, or smallcontainers thereof, to comminute the waste, but it is desirable to cutup tires into pieces having an average weight in the range from about50g-1 Kg, thus avoiding the cost of comminuting the tires into piecesweighing less. Means for cutting up tires are well known and any ofthese means may be employed with varying degrees of effectiveness, thoseproviding relatively smaller similarly sized pieces being easily fedinto and submerged in the molten lead.

Referring now to FIGS. 1-5, the system includes a feeding mechanism,referred to generally by reference numeral 90 (see FIG. 5), throughwhich waste W is fed to a reactor 10 housed in an insulated housing H(not shown in FIG. 1, see FIG. 4). Waste W is converted to hydrocarbonsin an elongated, heated vat 20 in the reactor, leaving a residue R whichis discharged first through a residue-discharging mechanism 60, andthereafter, to a residue-disposing mechanism 80. The waste W iscompacted and fed to the reactor 10 as a dense, tightly-packed mass of Wwhich functions as an effective air-tight seal to prevent entry of airinto the inlet end of the reactor. The waste W enters the vat on aninlet-incline 21 functioning as a feed-guide for waste and guiding it toflow beneath a first of at least two, and preferably five urging drums13, 14, 15, 16 and 17, each rotatably mounted on axially alignedsupporting shafts 18 and 18′ (see FIG. 2), one of which (18′) is apassive shaft, the other (18, not visible) driven by drive means such asan electric motor (not shown).

The reactor 10 preferably comprises a box-shaped reinforced steel casing11 having a roof 12, front and rear sidewalls 19 and 19′ (only rearsidewall 19′ is shown) and end walls E1, E2 all of which are insulatedto conserve heat within the reactor, and further protected by an outerinsulated structure (not shown in FIG. 1). The roof 12 is provided withremovably sealable covered hatches 12′ to allow catalyst to be chargedto the vat initially (before commencing operation of the reactor), andto permit servicing the reactor. In the vault above the vat 20, near thetop of rear sidewall 19′ are provided several laterally spaced-aparteffluent ducts “D” through which hydrocarbon vapors are ducted to avapor recovery system (not shown).

Heat to the lead in the vat 20, resting on an insulated base B, issupplied by a heating system including at least one array of plural,parallel, heating tubes 22 spaced-apart along the x-axis, and preferablymultiple parallel arrays, one disposed above the other, the heatingtubes of the one array being staggered relative to the other. The tubes22 are in open communication with side hot-air manifolds 23, 23′ (FIG.3) on either side of the vat, through which manifolds and tubes aheating medium is ducted, back-and-forth, until the heating mediumleaves the heating system. Preferably the heating medium is provided byhot gases generated by burners fueled by oil or natural gas. The detailsof the means for heating the lead in the vat are not narrowly criticalas long as the heating medium is supplied at a temperature above about650° C., preferably above 900° C. such temperature being provided by thehot gases. Sufficient lead is loaded into the vat so that when the leadis molten, its level “L” is preferably at least 10 cm above the uppersurface of the uppermost array of heating tubes in the bath. The moltenlead presents a planar surface extending from the vat's inlet end 24 toits discharge end 25.

A convenient size for the internal dimensions of a reactor is about 7.5m long ×1.2 m wide and 2.1 m high, the length of the bottom 26 of thevat corresponding to that of the bottom of the reactor.

Referring to FIG. 2, there is shown a hollow, acid-resistant steel drum14 with its axis of rotation along the x-axis in a mixing and bathingassembly 40. Drums 15, 16, 17 and 18 are similar to drum 14 and areabout equidistantly longitudinally spaced-apart from one and another(along the y-axis) inside the reactor. Because the amount of waste undereach successive drum 14-18 progressively diminishes as W is converted,the height at which each drum 15-18 is mounted within the reactor,decreases progressively. Thus, the axis of rotation of drum 14 is lowerthan that of drum 13; the axis of rotation of drum 15 is lower than thatof drum 14; the axis of rotation of drum 16 is lower than that of drum15; and so forth, drum 17 being mounted for rotation closest to thelevel L because substantially all the waste has been converted at thatpoint.

Each drum is independently rotatable and provided with its own mixingand bathing assembly 40. Drum 13 being positioned near the inlet of thereactor does not have a mixing and bathing assembly as its sole functionis to urge the waste under the drum 14. The height at which drum 13 ismounted depends upon the particular feed, being higher for polyolefinsheet and lower for scrap rubber. In general, the spacing of the lowersurface of the drum 13 from the surface of the melt L, is in the rangefrom 25-35 cm, and the spacing of the other drums, successively lower,the spacing of the lower surface of the last drum 17 being in the rangefrom about 10-15 cm above L.

The length of each drum (along the x-axis) is approximately the same asthe width of the vat 20 (along the x-axis), and each end of each drum14-17 has a cam-follower rod 41, 41′ (not shown) secured near thecircumference of each drum's end, the rods 41, 41′ projecting parallelto shafts 18, 18′, in the x-axis direction. The circumferential surface42 of the drum is provided with plural, generally laminar radialprojections 43, 44, 45, 46 (not visible) spaced-apart axially, in rowsalong the surface and staggered in spaced-apart relationship around thecircumference. As shown, four rows of projections are staggered at rightangles to each other, each pair of rows being positioned atdiametrically opposite ends. These projections are referred to as“mixing and urging blades”, more conveniently as “fingers”, becausetheir function is to mix the waste under the drum and urge the wasteaway from the drum, along the y-axis. Though the shape of each of thefingers is not narrowly critical, it is preferred they be relativelybroad at their straight edges 47, projecting radially, for maximumthrust efficiency. As shown in the schematic detail of a finger in FIG.2A, a strip 48 is welded at right angles to an arcuate piece 49 whichreinforces strip 48, and both are welded to the surface 42 of the drum.The arrow shows the direction of rotation of the drum. As the drumrotates, the leading edge of the arcuate reinforcing 49 moves throughthe waste and directs it against the strip 48.

A U-shaped saddle 30 having a grating 31 and sides 32, 33, is pivotablymounted with generally triangular flanges 34, 34′ (not shown) forrotation about a pivot rod 35. The grating 31 is provided with pluralparallel, spaced-apart slits 36. Each side 32 and 33 has a cam-opening37, 37′ of identical outline cut into each side, so as to allow therespective cam-follower rods 41, 41′ to ride the inside edges of eachcam-opening as the drum rotates. The rotation of the drum thus raisesand lowers the grating in a slightly angulated, generally verticaldirection, between an “up” position above the melt and a “down positionunder the surface of the melt. This motion simultaneously raises thefloating waste while heating it, and scoops Lip melt coming through theslits 36 so as to bathe the waste with melt. Preferably, the “up”position is about 5 cm above the melt's surface and the “down” positionis about 5 cm below the melt's surface.

To ensure that the waste is efficiently transferred from under one drumto the next, the radial length of the fingers is such that the tips ofthe fingers in each row sweep past close to the surface of the grating31. This action requires that the longest fingers 44 sweep the gratingwhen it is at its nadir (lowest point) in the melt, and that the fingers46 be shortest when the grating is at its apogee (highest point) abovethe melt. This is achieved by aligning the cam-follower rods 41, 41′with the longest fingers when the rods 41, 41′ are welded to the drum.

As waste W is mixed, bathed with melt and transported through thereactor, the waste is converted into C₁-C₂₄ ⁺ hydrocarbons, CO and CO₂which are removed from the reactor through effluent ducts D, leaving aresidue R. The R-discharging mechanism 60 and the R-disposing mechanism80 cooperate to provide an effective air-tight seal at the outlet end ofthe reactor.

It is seen that the R-discharging mechanism 60 comprises adischarge-incline 61 the lower edge of which commences at the upper edgeof the vat 20 at its outlet end 25. The upper edge of the incline 61terminates in a V-shaped saddle 62 in which the apex 63 is semicircularto cradle a discharge screw conveyor 64. Above the discharge-incline 61is proximally mounted an endless chain conveyor 64, having a drivecylinder 65 on which the chain is drivingly trained, and which chaingoes around stationary passive cylinder 66, the drive cylinder being atthe lower end of the conveyor. The vertical position of the drivecylinder 65 is adjustable by movement of a pivot arm 67 that isconnected to the drive cylinder with a link 68 so that the angle atwhich the chain conveyor operates is in the range from 1° to about 20°to the horizontal. In operation, the lower portion of the chain aroundthe passive cylinder 66 is about 5 cm above the upper edge of thedischarge incline 61, and the lower portion of the chain around thedrive cylinder is about 15 cm above the lower edge of the dischargeincline so that the chain is able to urge residue R up the dischargeincline and over its upper edge into the V-shaped saddle 62. The angleat which the chain conveyor is operated is chosen as a function of theparticular type and amount of residue R generated.

When residue R is dropped into the saddle 62, the screw conveyor 64pushes the residue R out of the saddle into the R-disposing mechanism 70(see FIG. 4) Referring to FIG. 4 there is schematically illustrated thescrew conveyor 64 driven by a motor M1 which drives the screw until itdrops residue R into a vented residue collection chamber 71 providedwith an overhead recycle duct 72 to recycle gases from the chamber 71 tothe environment in the reactor, above the vat 20. The chamber 71 hasmounted therewithin a manually operable (“hand-cranked”) paddle agitator72 which may be intermittently rotated to mix the residue and prevent itclumping up. The floor of the chamber 71 is provided with a centralsemi-cylindrical trough extending beyond the chamber as pipe 73 having adischarge outlet 74. A manually operated screw conveyor 73 is rotatablydisposed in the trough and extends into the pipe 73 so that when shaft75 of the screw conveyor 73 is rotated, residue is conveyed to thedischarge outlet 74 which is normally sealed against entry of air with agasketed sealing plate 75 and cooperating quick-opening andquick-closing clamp 76.

Intermittently, a residue-disposing means 80 is locked to the dischargeoutlet 74 to receive the residue. Preferably a sealable, wheeled cart 81is used, the cart having an opening 82 in the ceiling of the cart, andanother opening 83 in an endwall near the floor of the cart. Eachopening is provided with plates and quick-opening and quick-closingclamps which seal the interior of the cart against leakage of gas.Opening 82 is opened and locked to the discharge outlet 74 when the cartis to be loaded with residue R discharged from the collection chamber71. When the cart is locked in this position, the screw conveyor 73 isrotated, and residue R is discharged into the opening 82 of the cart.

Reverting to FIG. 3, it is seen that drum-supporting shafts 18 and 18′are supported in the sidewalls of structural insulated housing H (seeFIG. 4) that protects and insulates the reactor 10. The drum 17 is showwith only three fingers in each row, and the U-shaped saddle 30 is notshown so as to minimize confusion. Waste W is forced under the pluraldrums above the surface of the melt to which heat is supplied, firstthrough longitudinal heating tubes 27 under the melt, and then by pluralbanks of transversely disposed heating tubes 22 (see FIG. 1), the hotgases traveling from one bank to the next through the side manifolds,until ducted away from the reactor. Hydrocarbons are led from ducts D toa condenser where they are condensed to recover mainly some C₄ andessentially all the other components heavier than C₄. The level of thesurface of the melt is monitored by level control LC in one side 19 ofthe reactor.

Waste W may be charged to the reactor R with any conventional feedingmechanism 90 such as is illustrated in FIG. 5, provided the inlet to thereactor is sealed against entry of air. In the mechanism illustrated,waste W is dumped into a feed bin 91 from which it is discharged onto aendless conveyor 92 and into a waste-charging hopper 93 in opencommunication with a charging lock 94 defined by spaced-apartquick-opening and closing valves 95, 96. Valve 96 is positioned above aninitial waste-compressing feeder 97 adapted to feed the waste W to asingle-stage fluid-actuated press 100. A plate 98 is pivotably mountedbetween the feeder 97 and the press 100 for movement from a verticalposition (which allows waste to flow past the plate), to a horizontalposition, closing the lower opening of the feeder 97. A fluid-actuatedcylinder 99 opens and closes the plate 98.

After the waste W is initially compressed in the press 100, a ram 101compresses the waste horizontally and forces the W into and through aflanged connector tube 102 which connects the inlet of the reactor inopen communication with the press 100. With this arrangement it is seenthat the volume between the connector tube 102 and the inlet to thereactor is so densely packed with waste W that the waste forms anair-tight seal preventing entry of air into the reactor, and exit ofgases out of the reactor.

The invention described herein is further described by the followingspecific examples that are given by way of illustration and not as alimitation on the scope of the invention.

The following runs were made with (1) scrap polyolefin waste, mainly PEand PP; (2) scrap rubber obtained by cutting up worn automobile tires;(3) polystyrene; and (4) scrap Kraton® styrene-butadiene-styrene blockcopolymer, referred to as “SBS”. All runs use a mixture of the calcinedbauxite and aluminum powder in various proportions as catalyst. Themixture of waste and catalyst is fed in less than one minute, to a pilotplant scale reactor containing a molten lead bath maintained at about500° C. In each run, 1 Kg of the waste is mixed with 200 g of catalyst,to ensure maximum conversion. In the following Table 1, “% conversion”refers to the ratio of reusable hydrocarbons to waste fed, and theamounts of bauxite and Al powder are stated in grams. Most of thesehydrocarbons, which are recovered in a water-cooled heat exchanger, boilin the range from 40° C.-400° C.; the remaining hydrocarbons, in therange from C₁-C₄, are present in an amount less than 20% of thecondensed hydrocarbons. The cooling water used in the examples isrecycled after being air-cooled, for example in heat exchangers to heatoffices in the vicinity of the reactor, and enters the condenser at 30°C. Colder water will result in more C₅ ⁺ components being condensed, itbeing understood that conditions of pressure and temperature in thecondenser are such that predominantly C₅ ⁺ components condense in theliquid phase which is in equilibrium with vapors saturated with thecomponents. All runs are completed in less than 30 min, after which thereactor is allowed to cool and the residue recovered. TABLE 1 Ex. No.Waste Bauxite Al powder % Conv. 1 PE/PP none none 53 2 PE/PP 200 none(100% bauxite) 70 3 PE/PP none 200 (100% Al) 94 4 PE/PP 194 6 (3% Al) 975 rubber 200 none (100% bauxite) 40 6 rubber none 200 (100% Al) 55 7rubber 194 6 (3% Al) 53 8 polystyrene 194 6 (3% Al) 80 9 SBS 194 6 (3%Al) 40

It is evident from the foregoing data for conversions of bauxite and Alpowder, individually, that 97% bauxite and 3% by weight of pure Alpowder is more effective than pure Al powder by itself. One would expect(by ratioing yields of PE/PP obtained with bauxite and Al powder,individually) that 3/97 of Al/bauxite would yield 70.81% conversion.

Ratioing yields of scrap rubber obtained with bauxite and Al powder,individually, it is evident that 3/97 of Al/bauxite would yield 40.45%conversion, not 53%.

It is evident, that quite unexpectedly for each waste, the combinationof Al/bauxite produces a much higher conversion than calculated.

It is also evident that the same combination produces lower conversionsof scrap rubber, polystyrene and SBS rubber, than of PE/PP, but it iseconomical to process most such waste in the reactor because it yieldsat least 40% by weight conversion (of the waste fed) to C₅ ⁺hydrocarbons.

EXAMPLE 10 Molten Lead Bath Temperature: 465° C.-495° C.

1 Kg of PE/PP is mixed with 200 g of catalyst containing 97% calcinedbauxite and 3% Al powder, and fed to the bath in less than 1 min. Theeffluent vapors from the reactor were condensed in a water condenser(water temperature about 30° C.). Boiling points of the condensedhydrocarbons range from 210° C.-400° C. The weight of the condensate is930 g, indicating 93% conversion of PE/PP.

In an analogous manner, polyester from discarded beverage bottles andpolyamide, i.e. nylon scrap is also converted, though with lowerconversions.

EXAMPLES 11-13 Effect of Concentration of Al Powder on Conversion ofScrap Rubber from Vehicle Tires in Various Temperature Ranges:

1 Kg of the scrap rubber in pieces each weighing less than 50 g, andwith strands of wire still in the rubber, is mixed with 200 g ofcatalyst containing the stated amounts (in grams) of calcined bauxiteand Al powder, and fed to the bath in less than 1 min. The effluentvapors from the reactor were condensed in a water condenser (inlet watertemperature about 30° C.). Boiling points of the condensed hydrocarbonsrange from 235° C.-400° C. In the following Table 2, the weights ofbauxite, Al powder and the condensate collected, is given in grams, andalso as “% conversion” (% of rubber fed). TABLE 2 Ex. No. Bauxite Alpowder % Al Temp. ° C. Condensate % Conv. 5 200 none 0.0 490-520 400 4011 197 3 1.5 500-520 400 40 7 194 6 3.0 490-520 530 53 12 190 10 5.0490-520 520 52 13 185 15 7.5 485-520 550 55 6 none 200 100 490-520 55055

It is evident from the foregoing data that maximum conversion of rubberat the stated temperature is obtained with from about 3-10% by weight ofAl powder.

Having thus provided a general discussion, described the overall processand apparatus in detail and illustrated the invention with specificexamples of the best mode of carrying out the process, it will beevident that the invention has provided an effective solution to an oldand difficult problem. It is therefore to be understood that no unduerestrictions are to be imposed by reason of the specific embodimentsillustrated and discussed, and particularly that the invention is notrestricted to a slavish adherence to the details set forth herein.

1. A process for the pyrocatalytic conversion of a predominantlyhydrocarbon waste comprises, feeding the waste, substantially free of ahalogen-containing synthetic resinous material, into a bath of moltenlead held at a temperature in the range from about 400° C. to 600° C. inan elongated vat confined in a reaction zone having an essentiallyoxygen-free atmosphere; mixing the waste with a catalyst in an amount nomore than 20% by weight of the waste fed, the catalyst consistingessentially of a major proportion by weight of particulate aluminumoxide mineral having particles <2 mm in equivalent diameter, incombination with a minor proportion of essentially pure aluminum powderhaving substantially all particles having an equivalent diameter <0.1mm; urging the waste along the vat's longitudinal axis while contactingthe waste with the molten lead; thermally and catalytically convertingthe waste with at least 50% effectiveness into reusable hydrocarbonvapors and carbonaceous residue; removing the reusable hydrocarbonvapors from the reaction zone; and, removing the carbonaceous residuefrom a residue-discharging zone.
 2. The process of claim 1 wherein thewaste is selected from the group consisting of a polyolefin, poly(vinylaromatic), polystyrene, polyamide, rubber derived from a conjugateddiene, the diene having from 4 to 5 carbon atoms, and rubber defined asa polyblock copolymer of a vinylaromatic compound and a conjugateddiene, optionally hydrogenated to include a block of a monoolefin, theolefin having from 2 to 4 carbon atoms; and, recovering the reusablehydrocarbons consisting essentially of a major proportion by weight ofC₅ ⁺ hydrocarbons and a minor proportion of C₁-C₄ hydrocarbons.
 3. Theprocess of claim 2 wherein residence time for the waste in the vatbetween its waste-charging end and its residue-discharging end, is nomore than one hour, and including, recovering a condensate consistingessentially of C₅ ⁺ hydrocarbons.
 4. The process of claim 3, includingfloating a layer of the waste on the molten lead near the waste-chargingend of the vat; and, wherein the aluminum mineral oxide is selected fromthe group consisting of a calcined hydrated aluminum oxide and azeolite, and the condensate of C5⁺ hydrocarbons is at least 40% byweight of the waste fed.
 5. The process of claim 4 wherein the hydratedaluminum oxide temperature of molten lead is in the range from about450° C. to 550° C., and is maintained by passing a fluid heating mediumthrough plural ducts transversely disposed relative to the longitudinalaxis of the vat, and the temperature of the heating medium under themolten lead's surface near the waste-charging end of the vat is above600° C.
 6. The process of claim 5 wherein the heating medium is hot gas,and the waste in the vat is unconfined except by the surface of themolten lead.
 7. The process of claim 6 wherein mixing and transport ofthe waste in the molten lead is effected by plural spaced apart,rotatable, first, intermediate and last mixing drums successivelyarrayed in generally parallel relationship, each also verticallyspaced-apart from a preceding drum at a lower axial position than thepreceding drum so as to effect transfer of the waste from point of entryinto the reactor until the waste is moved as residue to a location underthe last drum.
 8. The process of claim 6 comprising removing the residuein the residue-discharging zone with an endless conveyor urging theresidue upwards along an incline to a residue-disposing means.
 9. Theprocess of claim 8 wherein the endless conveyor is adjustably operableto exert pressure on the residue, the conveyor being drivingly trainedabout a first drum having a vertically adjustable axis of rotation,adjustable over the residue-discharging end of the vat, and a seconddrum having a fixed axis of rotation, proximally disposed to theincline's upper surface.
 10. A system for the conversion of organicwaste essentially free of a halogenated synthetic resinous material intoreusable hydrocarbons, the system comprising, a feeding mechanismincluding a conveyor means to feed the waste into an inlet orwaste-charging end of an elongated vat adapted to hold molten lead at atemperature in the range from about 400° C. to 600° C.; a pyrocatalyticreactor having the vat disposed therein, the vat having a substantiallyplanar bottom member terminating in opposed inlet and outlet endwalls,the inlet endwall terminating in the waste-charging end of the vat, andthe outlet endwall terminating in the residue-discharging end of thevat; a residue-disposing mechanism cooperating with the residuedischarging end of the vat; at least one (first) heating arraycomprising plural adjacent heating conduits or ducts adapted to carry aheating fluid at a temperature above about 600° C. under the moltenlead's surface near the waste-charging end of the vat; at least tworotatable drums each disposed for rotation about an axis essentiallyorthogonal to the longitudinal axis of the vat, and in vertically-spacedapart relationship with the molten lead's surface, the drum having amultiplicity of radially protruding mixing and urging fingers adapted tomove the waste through the molten lead towards the residue-dischargingend of the vat; a generally U-shaped saddle having a rectangular gratingdisposed directly beneath the drum, the grating lying parallel to thelongitudinal axis of the drum, the saddle being pivotably disposed aboutan axis coaxial with that of the drum; means cooperating with the drumto reciprocate the grating; a vault above the vat, for collectinghydrocarbon vapor, carbon monoxide, carbon dioxide and other gases, thevault's lower edges being sealingly secured to the vat in gas-tightrelationship therewith; and, duct means for removing gases from thevault.
 11. The system of claim 10 wherein plural spaced apart, rotatablefirst, intermediate and last mixing drums are successively arrayed inparallel relationship, each also vertically spaced-apart from apreceding drum at a lower axial position than the preceding drum so asto effect mixing of the waste at the molten lead's surface under thelast drum.
 12. The system of claim 10 wherein residue-dischargingmechanism comprises an endless conveyor to urge the residue upwardsalong an incline, the conveyor being adjustably operable to exertpressure on the residue as it is urged upwards so as to compress theresidue and provide a substantially gas-tight seal between the conveyorand the incline's upper edge, the conveyor being drivingly trained abouta first drum having a vertically adjustable axis of rotation disposedover the residue-discharging end of the vat, and a second drumproximally disposed to the incline's upper edge and having a fixed axisof rotation.